In this post I want to explain what Docker is, in such a simple way, so that every vSphere Admin would get it in seconds :) I was initially having a difficult time understading the value of Docker (vs VMs) etc, but I think the analogy i’ve come up with should be quite simple.
The TL;DR version of what docker is, simply put – Docker is the new shiny linux based Thinapp, for not-necessarily-end-user applications but more for dev apps – DBs, Backends, etc
YES. I’ve said it, and i’ll repeat, docker, in my eyes, is VERY comparable to Thinapp / Appv / any other application virtualization software.
What docker aims to do initially, is to help applications delivered seamlessly throughout environments using something called LXC / or Linux Containers, which are essentially a method of isolating application processes within linux, dictating which resources are and aren’t available for your specific app.
In a sense, this is exactly what Thinapp / Appv had tried to do in the past, only for the EUC market. You take IE6, you install it in an isolated ‘fake’ environment (with fake registry, face C: , etc) , and there you go. you can deploy it on any windows OS.
Essentially, when you build a Dockerfile, used to create docker images, you are doing the same. You decide on a base OS, with statements like :
or any other OS you wish to build your application on. Then, you describe how your app is installed, whether its running scripts, or yum commands, using the different tools docker provides you with like environment variables etc. So commands like:
“RUN yum install httpd” for example, depict what is necessary to dockerize an apache web server.
Lastly, you create the endpoint for the running container. Meaning, you select which ‘.exe’ should run when the container is started (for those of you who’ve used thinapp) so in linux, you should see something like running a script, starting a service, or running a binary file.
So now, I can build my apache web server docker image, using my Docker file, and run it on any linux distro I want to, since the dockerized apache *thinks* its running on ‘centos7’ using the centos image (which is essentially the centos libraries, and linux filesystem structure) and using the same linux kernel.
That’s why containers best practices dictate its better off to run a single process in a container, since its just virtualizing an app for its OS environment. In that sense, Dockers and VMs are not contrasts at all. VMs, solve an operations issue, for an OS being dependent on hardware, and Docker, solves a developer issue, for an App being dependent on a specific linux OS, or OS packages.
So to finalize my weird but valid (IMO) comparison, if linux had IE6, using docker, you could run IE6 & IE 7 at the same time without any OS issues.